CM measurement: residual moisture screed 2.1 to 2.3%

Hello everyone,
yesterday a CM measurement was carried out in my screed with underfloor heating in one room, showing a residual moisture content of 2.1%. In the other rooms, a residual moisture content of 2.1 to 2.3% was measured using a moisture meter. My floor fitter wants to lay design flooring next week and said the values are okay. However, I have read that the residual moisture may only be a maximum of 1.8%. What is your opinion on this matter? Thank you for your feedback.

Hello, lars-steina, The correct value (I assume a cement screed) is, as you correctly assumed, 1.8%, measured with the CM device. A measurement with another device (e.g. electrical resistance measurement) would be invalid in case of dispute. His argument may be based on the assumption that the screed will continue to dry sufficiently until the actual installation date. In general, the floor layer is responsible for testing the substrate. If he does not test, or makes incorrect decisions based on the test, he is of course liable for it. Despite his liability, I strongly advise you not to install with these values anyway. Because all the inconveniences of a complaint remain. The design covering (vinyl planks) is a vapor-impermeable floor covering, i.e. overnight drying leads to more risks than with diffusion-open floors. If you have underfloor heating, the correct heating is of course also mandatory! ([Aufheizprotokoll]) In summary: Do not install at elevated values, anything else would be botched work... Best regards Wieli